Preliminary results indicate that increased food availability to young rats results in an increased rate of morphological and functional development. Such changes will be studied further. Using micropuncture techniques, superficial single nephron glomerular filtration rate as well as overall glomerular filtration rate will be estimated in control and experimental animals with high food availability. Glomerular structure along with morphological studies of tubular structure will be done at both the light and electron microscopic levels. An estimate will also be made of the fraction of glomeruli filtering, i.e., having become mature. finally, the relationship between single nephron GFR and proximal tubular length will be studied in the two populations of animals.